According to the prior art, this lighting of the rear face is carried out by means of an unpolarized light source 1. This source can be neon tubes associated with optical devices for rendering the luminous flux uniform. Another technology uses light-emitting diodes, associated with complex optics able to mix the light of the various diodes to provide an extended uniform flux of white light.
The light source provides an extended light flux L towards the entrance polarizer P1 of the screen CXL. The entrance polarizer thus absorbs theoretically 50% of the light emitted by the source L (dichroic polarizer), and lets through only the light in the corresponding polarization of that of the polarizer. In fact, and as shown diagrammatically in FIG. 2, the actual rate of light transmission by the entrance polarizer is of the order of 40% of the light flux L emitted by the source, on account of transmission losses in the entrance polarizer. For these reasons, powerful sources, having high electrical consumption, are necessary for producing high-luminance displays.